Noise levels generated by modern commercial aircraft during take-off and landing are of significant importance to aircraft operators. In order to reduce (to attenuate) the noise emitted by aircraft engines, the air intake passages of gas turbine or turbofan engines are generally provided with acoustic liners on the inner surfaces of the engine which are configured to attenuate the noise generated by the engine in operation.
Various designs of noise attenuating panel are known in the art. Generally, the panels comprise a perforated layer defining part of the inlet passage of the engine and a further imperforate layer defining the back of the panel. A honeycomb layer, such as that manufactured by the company Hexcel, is located between the two layers. Thus, noise can be attenuated by the honeycomb layer as air is permitted to enter the honeycomb through the perforated panel.
These existing acoustic panels have resulted in significant improvements in aircraft noise levels. However, with desired increases in fuel economy from aircraft operators the additional weight known acoustic panels add to aircraft engines presents its own problems. One solution to reduce weight is to employ a lighter material such as composite materials. Moving to acoustic panel manufacture using composite materials can mitigate the additional weight problems of acoustic panels. However it significantly increases the cost and complexity of acoustic panel manufacture owing to the nature of composite part manufacturing.
The present invention aims to address the problems associated with the prior art in terms of weight whilst providing an improved acoustic panel at minimal manufacturing cost. This can thereby reduce fuel consumption of the engine and minimise energy use in manufacturing.